The present invention relates to a connector, and more specifically, to a microwave connector for efficient thermalization and filtering of microwave lines at millikelvin temperatures.
The use of high-frequency coaxial lines at cryogenic temperatures (i.e., temperatures below 1 K) presents a number of experimental difficulties. These difficulties are mainly related to the proper filtering of unwanted frequencies, adequate impedance matching of circuit components and optimal thermalization of the lines.
Experiments in the GHz frequency regime normally impose stringent conditions on the bandwidth within which the experiments are performed. Out-of-band spurious radiation tends to be unacceptable and proper filtering is therefore a must. Likewise, to avoid reflections of the experimental signal, which can result in signal loss, standing waves and added noise, impedance matching of all the connectors and components in the circuit is important.
For typical cryogenic setups, thermal conduction from room temperature down to the coldest stage of the refrigerator must be minimized, and thus most popular choices of coaxial lines for high frequency measurements at low temperatures involve the use of good thermal isolators like superconductors. At the same time, proper thermal anchoring of the lines at each stage of the refrigerator is a must. In coaxial lines, for example, whereas the outer conductor presents no problems for heat sinking, the efficient thermalization of the inner conductor constitutes a significant challenge, as the dielectric separating outer and inner conductors is typically an excellent thermal insulator. Different solutions exist to solve this problem, like λ/4 studs, cold attenuators, or striplines encased in epoxy, amongst others. These approaches, however, may present added difficulties in some experiments. A λ/4 stud, for example, has a very low bandwidth, whereas the effectiveness of cryogenic attenuators at millikelvin temperatures for inner conductor thermalization is somewhat unclear. Epoxy stripline filters tend to be bulky in order to avoid the dissipative side walls of the encasing to alter the field lines.